The invention relates to a combination of a borated ashless dispersant and a solvent oil especially useful in gasoline fuels for alleviating an abnormal combustion phenomenon of spark ignition engines. More specifically, it relates to a combination of a borated nitrogen containing dispersant known as a lubricating oil additive to improve the sludge dispersancy property of lubricating oils and a mineral oil which is added to gasoline fuel to alleviate dieseling in spark ignition engines, a phenomenon which occurs when said engine continues to run when the ignition is turned off.
Basically, an automotive engine is an energy converter, releasing mechanical energy or power in two related steps. First, the chemical energy in gasoline is converted to heat energy by burning the gasoline in the engine's combustion chambers. Secondly, some of this heat energy causes the combustion gases to expand, forcing each of the pistons down and producing mechanical power.
For efficient power production, the conversion of chemical energy to heat energy must occur in an orderly fashion at the proper time in the engine cycle. In a normal engine cycle, the spark-ignited flame spreads across the combustion chamber burning the gasoline smoothly and compressing the unburned fuel-air mixture ahead of it. In addition to being compressed, the "end gas" ahead of the flame front receives heat radiated from the advancing flame. If the end-gas temperature and pressure remain below critical levels, the flame front will consume all the fuel in a uniform manner providing normal combustion. Unfortunately, various factors including engine design and operation and combustion-chamber deposits may act to produce abnormal combustion; a process wherein a flame front is started either prior to or after spark ignition and includes a condition in which the fuel charge is consumed at extremely high rates.
Abnormal cumbustion can be categorized into: spark knock which is recurrent and repeatable in terms of audibility and controllable by spark advance; surface ignition whereby the fuel-air charged is ignited by overheated valves, spark plugs, glowing combustion-chamber deposits or any other hot spot in the combustion chamber; and, dieseling (also known as run-on and after-run).
Surface ignition is an uncontrolled ignition which may occur before the spark plug ignites the charge (preignition) or after normal ignition (postignition). This abnormal combustion can lead to power loss, engine roughness, knock and other audible noise, runaway ignition and destruction of engine parts. To prevent uncontrolled ignition of the fuel by glowing combustion-chamber deposits and sparkplug fouling by engine deposits, deposit modifiers such as alkyl or aryl phosphates, alkyl phosphines and alkyl borinates have been reported as added to gasolines to alter the chemical compositions of the deposits making them less likely to glow and thereby cause uncontrolled fuel ignition. U.S. Pat. No. 2,975,135 teaches that lead-carbonaceous deposits can be attacked by incorporating a fuel soluble organic boron compound in a liquid leaded motor fuel (column 1, lines 48-50).
Dieseling is an abnormal combustion phenomenon that occurs when a spark ignition engine continues to run after the ignition is turned off. This problem has existed for many years and has been widely investigated. However, dieseling seems to be occurring more frequently with late-model cars, particularly when these cars operate on low-octane gasolines. A vehicle study, reported in "SAE Transaction", Volume 81, 720085 entitled "Influence of Engine Fuel Factors on After Run" by J. Bensen of the General Motors Corp., was conducted to gain a better understanding of the factors that influence after-run. Engine operating variables, such as high idle speed, lean idle mixture, and retarded basic spark timing, all increased after-run frequency by increasing the throttle opening (intake charge density). Reduced Research-octane number (RON) of the gasoline also increased after-run frequency, but Motor-octane number (MON) and hydrocarbon composition did not have any effect. The author concluded that after-run, i.e., dieseling, is probably caused by compression ignition rather than surface ignition, and may be related to high-charge density in the cylinders after the ignition is turned off. He suggested only a mechanical method of preventing after-run which was to install an "anti-dieseling solenoid," an electromechanical device that closes the throttle when the ignition is turned off. He also concluded that preventing after-run by adjusting engine-operating variables conflicts with current automobile exhaust emission-control systems that require high idle speeds, lean mixtures, and retarded spark timing.
Dieseling also represents an environmental hazard since after-run exhaust is reported to contain about 125 times more aldehydes than engine idle exhaust, cause eye irritation and has an obnoxious odor.
The addition of boron-containing substances to the combustion chamber of spark ignition engines is further exemplified by U.S. Pat. No. 3,303,208 which teaches the introduction of metaborate ester-amine reaction products by addition to gasoline; U.S. Pat. No. 3,000,916 which teaches that boron levels of 10 to 20 parts per million in gasoline of a borated reaction product of an N-alkyl alkylene polyamide with a polymeric long-chain unsaturated polybasic carboxylic acid provides excellent rust inhibition; and, U.S. Pat. No. 2,725,857 which teaches that the surface deposits of combustion chambers can be reduced by coating the combustion chamber surfaces with a coating containing an inorganic boron compound, such as copper borate, by introduction of the composition through the sparkplug openings of the engine. It is also known that borated oil additives are excellent sludge dispersants as seen in U.S. Pat. Nos. 3,087,936, 3,254,025, 3,281,428 and 3,282,955.
The additives of the prior art and particularly the additives which have been taught and useful for the addition to gasolines appear to have little or no effect on the dieseling type of abnormal combustion phenomenon, however, they do reduce the RON of the gasoline by their presence. This suggests that with the lower octane number of the gasolines being offered in today's market because of the obligation of reducing the tetraethyl lead content, there will be a greater tendency for dieseling to occur. Should the ignition timing be retarded to avoid detonation, there would be the additional tendency for run-on because of the higher exhaust system temperatures, higher operational temperatures of the engine and higher temperatures of the liquid coolant. The individual effect of each of these factors may well be small but together they promote dieseling in today's spark ignition engines.
In view of the foregoing, there is an urgent need to provide an anti-dieseling additive for gasoline and/or lubricating oils to be used in spark ignition engines, particularly in view of the decreased RON of the gasoline and the use of smaller engines to converse fuel for such engines are not susceptible to material retardation of spark timing in order to prevent dieseling.